A power converter converts power from one form (voltage, current, etc.) to another form more suitable for a specific application. A typical power converter consists of a semiconductor device that manipulates power flow. Example power converter types include a buck converter, a boost converter, and a buck-boost converter. A buck converter is used to step down the input voltage. A boost converter is used to step up the input voltage. A buck-boost converter acts both as a boost converter and a buck converter. Thus, a buck-boost converter is used to step up or step down depending on the control signals.
A power converter may be classified as switched mode or as non-switched mode. The semiconductor devices in non-switched mode power converters operate continuously. A switched mode power converter employs semiconductor devices as switches. The semiconductor devices are switched at a high frequency and their state (on or off) is determined by external signals sent from a controller. Because it is switched at a high frequency, the power flow is determined by the average time spent by the device in an on state as compared to the off state. By varying the amount of time spent by the switch in the on state as compared to the off state during a single switching cycle, the average properties of the power flow can be controlled.
Power converters often include multiple power converter modules that are arranged in parallel. Instead of a single power converter, multiple power converter modules are connected to supply a common load. The power converter modules provide power to a common load from a common source. Thus, the inputs and the outputs of the power converter modules are tied together, respectively. Paralleled power converter modules generally are used in high power applications of greater than one kilowatt, for example, in data servers, in electric vehicle drives, etc.
Power flow through a conductor has associated losses that are dissipated as heat. Thus, power flow through the power converter generates heat. Excessive heating detrimentally affects each power converter module causing it to age and possibly to fail prematurely. Based on statistical thermodynamics, it is well established that, for every 10° C. rise in average temperature, the lifetime of the power converter module is reduced by a factor of two. Thermal load cycling and the resulting induced cyclical stress on the power converter module can be major factors leading to failure of the power converter.
Power converter modules are expected to be rugged and to withstand severe external stresses. The semiconductor devices in switched mode power converter modules have a high thermal sensitivity. As a result, the heat must be removed efficiently to prevent failure or even destruction of the device. Different modules may undergo different environmental conditions leading to differential heat dissipation that in turn leads to some modules running hotter than the others. Some of the causes of differential heat dissipation are dirty heat sinks, poor air flow over some modules, geometric asymmetries, and different ambient conditions. To maintain acceptable reliability levels, existing approaches significantly over-design the system and add redundancy. These approaches can greatly increase the cost, the size, and the weight of the power converter and degrade the life time, mean time to failure, reliability, and availability of the power converter.
To prevent over designing and avoid the consequent costs while maintaining the same reliability, the relative temperature of the power converter modules should be controlled. Thus, if one module is operating at a higher temperature in comparison to the other modules, that module should be allocated a reduced load to generate less heat thereby lowering its operating temperature. In response, the load of the remaining modules increases to maintain support to the common load. In some power converters, the temperature of the modules is actively monitored using sensors. Such systems require additional communication channels, cables, and temperature sensors. The result is increased system cost and complexity and potentially degraded reliability. What is needed therefore is a system and a method that provide the temperature of a power converter module to allow thermal load management. What is further needed is a system and a method that provide the temperature of the power converter modules without use of additional communication channels, cables, and/or temperature sensors.